Cobalt-base alloy suitable for spray hard-facing deposit



United W6 a ent COBALT-BASE ALLOY SUITABLE FOR SPRAY HARD-FACING DEPOSIT Jerome K. Elbanm, Kokomo, Ind., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed May 12, 1959, Ser. No. 812,586

4 Claims. (Cl. 75-171) This invention relates to a cobalt-base alloy, and more particularly, to a cobalt-base alloy suitable for depositing by spray hard-facing techniques to other base metals or alloys for producing a hard, wear-resistant surface there- Spray hard-facing is a method by which a wear-resistant coating is deposited on a base metal or alloy by applying a hard facing alloy in the form of powder and subsequently applying heat to cause a metallurgical bonding between the base metal or alloy and wear-resistant coating applied thereto.

in spray hard-facing processes, the surface of the base metal or alloy is cleaned thoroughly, for example, by machining, sand-, or shot-blasting. The alloy to be deposited on the cleaned surface is reduced to a powder by any of the commonly-known techniques. This powder is suspended in a gas stream and passed through a heating means, for example, an oxyacetylene flame. The alloy powder becomes plastic in nature as it passes through the heating means and the force of the gas stream propels the powder, in this plastic state, against the base metal or alloy. When the sprayed alloy comes into contact with the base metal, the impact causes a primarily mechanical bond to form between the base metal and the alloy material but some diiiusion may occur and result in the formation of a metallurgical bond. Heat is subsequently applied to fuse the alloy to the base metal or alloy and thus insure complete metallurgical bonding between the alloy material and the base material.

Spray hard-facing techniques have been successful employing such metals or alloys as aluminum, copper, lead, nickel, zinc, brass, bronze, Monel metal, and stainless steel, either as the coating material or the base material.

However, heretofore it has not been possible to employ spray hard-facing techniques to deposit cobalt-base alloys on other metals or alloys because of a failure to obtain a satisfactory bonding between the cobalt-base alloy and the surface on which it was being deposited.

Accordingly, it is an object of this invention to provide a new cobalt-base alloy.

Another object of this invention is to provide a new cobalt-base alloy that can be deposited on other metals and alloys by spray hard-facing techniques.

Still another object of this invention is to provide an improved process for producing a hard, wear-resistant cobalt-base alloy surface deposit on other metals and alloys by spray hard-facing techniques.

Other aims and advantages of this invention Will be apparent from the following description and appended claims.

In accordance with this invention, a cobalt-base alloy is provided that contains, by weight percent, 15 to 30 chromium, 2 to tungsten, 0.8 to 3.0 silicon, 1.5 to 5.0 boron, up to 5 percent in the aggregate of at least one metal selected from the group consisting of iron, nickel, vanadium, and molybdenum, up to 0.3 carbon, and the balance cobalt and incidental impurities.

The cobalt-base alloy of this invention possesses the necessary oxidation resistance and fluidity when heated to permit its use in spray hard -facing techniques. It is believed that the unique combination of properties of this alloy may be because of the synergistic effect of the com-v Element: Weight percent Chromium 19.0 to 25.0. Tungsten 4.0 to 5.0.

Silicon 1.0 to 2.0.

Boron 2.0 to 3.5.

Iron

Nickel Up to 3 percent in Vanadium the aggregate.

Molybdenum Carbon Up to 0.3.

Cobalt and incidental impurities Balance.

Within these limits the alloy composition can be adjusted to obtain the most advantageous combination of properties. For example, an alloy containing, by weight percent, about 20 chromium, 4.5 tungsten, 1.2 silicon, 2.5 boron, up to 0.1 carbon, and the balance cobalt and incidental impurities has been found to have a desirable combination of good tensile strength, impact strength, and hardness.

The presence of metallic elements, such as iron, nickel, vanadium, and molybdenum, can be tolerated in an aggregate in amounts of up to about 5 percent and preferably not more than about 3 percent. These materials can be introduced through normal melting practices. Incidental impurities, such as sulfur, oxygen, phosphorus, copper, etc., introduced through normal melting practices, should be kept to a minimum. Particle size is critical only in that the maximum size and distribution of particle sizes will work satisfactorily in the equipment being used for the application. In general, we have found that all material should pass through a IZO-mesh screen so that satisfactory recovery can be achieved. It is preferred the particles are not so small that they will pass through a 270-mesh screen. The amount of fines which can be present and still permit successful spraying is primarily dependent upon the type of equipment used.

The cobalt-base alloy may be prepared by ordinary melting technique, such as induction melting, arc melting, etc. For example, chromium, tungsten, silicon, cobalt, and prealloyed cobalt-boron material, in suitable proportions, may be placed in an induction furnace in a magnesia crucible and heated until molten. The melt is then poured into water to produce small particles or shot. The portion of the shotted material that is not of a sufficiently small size is reduced in particle size by any of the commonly-known techniques.

The cobalt-base alloy of this invention can be deposited by spray hard-facing techniques on any metal or alloy normally amenable to spray hard-facing.

Several cobalt-base alloys were prepared and deposited on a mild steel base. The alloys were prepared by melting tungsten, silicon, cobalt, and a prealloyed cobalt-boron material in the desired proportions in a magnesia crucible and heated until molten. The melt was poured into water to produce small particles or shot." The portion of this Patented Nov. 22, 1960 Table 1 Weight Percent Element Alloy Alloy A110 y A llo y No.1 No. 2 No.3 No. 4

Chromium 24.17 19. 19 21. 07 23.97 4. 55 4. 55 4. S 4. 43 2. 68 2. 24 2. 72 3.05 1.32 1.26 l. 98 1.90 0.28 0. 25 0.28 1. 23 0. 05 0. 04 0. 04 0. 10 Cobalt and Incidental Impurities Balance Balance Balance Balance Hardness: Rockwell C 52-55 45-48 53-55 53-54 The hardness of the alloy may be adjusted by controlling the chromium and boron content. Increasing the amount of chromium and/ or boron will increase the hardness of the alloy.

The alloy of this invention may also be used as an alloy deposit to give a hard, wear-resistant surface deposit on metals and alloys by applying this alloy by any of the commonly-known and used techniques, e.g., by using a suitable lacquer base with the powder particles suspended therein, or by spreading the alloy on a base metal surface and heating to fuse the particles to the metal surface, or

by preparing the alloy in the form of a rod and depositing by welding technique.

This material is also amenable to fabrication by ordinary powder metallurgical processes, and to the production of shapes by casting.

What is claimed is:

1. A cobalt-base alloy containing, by weight percent, 15 to 30 chromium, 2 to 10 tungsten, 0.8 to 3 silicon, 1.5 to 5.0 boron, up to 5 percent in the aggregate of at least one metal selected from the group consisting of iron, nickel, vanadium, and molybdenum, up to 0.1 carbon, and the balance cobalt and incidental impurities.

2. A cobalt-base alloy containing, by weight percent, 19 to 25 chromium, 4 to 5 tungsten, 1 to 2 silicon, 2 to 3.5 boron, up to 3 percent in the aggregate of at least one metal selected from the group consisting of iron, nickel, vanadium, and molybdenum, up to 0.1 carbon, and the balance cobalt and incidental impurities.

3. A cobalt-base alloy containing, by weight percent, about 20 chromium, 4.5 tungsten, 1.2 silicon, 2.5 boron, up to 0.1 carbon, and the balance cobalt and incidental impurities.

4. A cobalt-base alloy containing, by weight percent, about 21 chromium, about 4.6 tungsten, about 2 silicon, about 2.7 boron, 0.04 carbon, and the balance cobalt and incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,849 Grossman July 11, 1939 2,855,295 Hansel Oct. 7, 1958 2,868,667 Bowles Jan. 13, 1959 

1. A COBALT-BASE ALLOY CONTAINING, BY WEIGHT PERCENT, 15 TO 30 CHROMIUM, 2 TO 10 TUNGSTEN,0.8 TO 3 SILICON, 1.5 TO 5.0 BORON, UP TO 5 PERCENT IN THE AGGREGATE OF AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF IRON, NICKEL, VANADIUM, AND MOLYBDENUM, UP TO 0.1 CARBON, AND THE BALANCE COBALT AND INCIDENTAL IMMPURITIES. 